Indeed we do! Regardless, 15/16" Altecs need big cabs to go low, so 9-10 ft^3 is the ideal minimum for decent LF response, with up to 20 ft^3 required for some versions when driven by a high output impedance amp.

I recently mused about what the trade-offs would be, MLTL's vs. Onken with Altec 414... What are your thoughts on this?

It got me curious coz I heard this enclosure design http://www.t-linespeakers.org/projects/yves/index.html
used with JBL 2213 (found in L100 monitors) in a buddy's system, and LF response is really good IMO even if the JBL's parameters isn't really that close to the Audax. The design was intended as a 'sub', so I think he used more stuffing as the JBL's still had good tonality up to the mids. Incidentally, the Audax T/S that were used in the TL's is quite close to the 414's. But with recent better predictive software like MJK's sheets, I think this 'traditional TL' could be improved upon...